Where did this gloriously twisted thing come from? Good gawd. The ending is delicious horror! It looks like a kid's cartoon... then it gets more and more unpleasant... then WHAM, gleefully-welcomed death and desecration! A knockout bit of obscure weirdness.
The mystery is revealed.
This is a Nazi cartoon, seized by the US in WWII.
The original is in color - but in its native German, it's not nearly as creepy as the gonzo English version available here at the archive. The opening 3D shot, according to some sources, infringes on patents held at the time by Max Fleischer.
The complete story (thanks to the web research of Michelle Klein-Hass):
The original version is on YouTube, in color and German: